In recent years, public attention has heretofore been focused on a fuel cell that serves as an electric power supply with a high energy conversion efficiency and minimal amount of exhaust emissions, such as carbon dioxide, and therefore has applications not only in automotive vehicles but also in general industrial fields or in domestic uses in a wide range. Such a fuel cell is operative to achieve electrochemical reaction using hydrogen and oxygen to obtain an electric energy and, to this end, various research and development works have heretofore been made.
Japanese Patent Publication No. 2735396 discloses a startup method for a fuel cell system. In such a startup method, when the fuel cell system is started up, an output voltage of a fuel cell is monitored during supply of fuel and air to the fuel cell and, when an output voltage level goes beyond an allowable lower limit value, electric power output is taken out form the fuel cell in correspondence with a load.